Can't see any of my photos in iPhoto for Mac

Question

I've had an iMac Late 2012 for two years. Since then, I've kept all my photos from my camera and my iPhone in the iMac's iPhoto app.
For some months, I'd been having a constant problem: The events' icons were empty and it said the event's name and that it had 0 photos (each one had lots of photos). However, if I double clicked on the event, I could open it and I could see all the photos correctly.
But, since last week I have a very serious problem with iPhoto. When I open iPhoto, it says something like how to import photos (as if I hadn't ever used it before), all my photos, events, etc. are gone. However, I realized something that maybe didn't make me so sad. I went to Finder > Photos > iPhoto library, I right clicked it and selected "Show information" (I'm from Argentina and my Mac is in Spanish, so I'm trying to translate the things of the Mac to English the best I can), and Finder says its size is 86 GB (so I hope all my photos and videos are here!!!).
Extra data: 1. I right clicked the iPhoto Library folder in Finder and chose Show the content of the package, and there are two folders with the iPhoto Library icon called: Library.iPhoto and Library 6.iPhoto, both size is 22 bytes. Maybe could help you realize which is the problem.
2. I also tried to updating my Mac to the last beta version, but the Photos app didn't solve my problem.
That you sooooo much for your help,
Greetings,
Nicolas.

Answer 1

Option 1
Back Up and try rebuild the library: hold down the command and option (or alt) keys while launching iPhoto. Use the resulting dialogue to rebuild. Choose to Repair Database. If that doesn't help, then try again, this time using Rebuild Database.
If that fails:
Option 2
Download iPhoto Library Manager and use its rebuild function. (In early versions of Library Manager it's the File -> Rebuild command. In later versions it's under the Library menu.)
This will create an entirely new library. It will then copy (or try to) your photos and all the associated metadata and versions to this new Library, and arrange it as close as it can to what you had in the damaged Library. It does this based on information it finds in the iPhoto sharing mechanism - but that means that things not shared won't be there, so no slideshows, books or calendars, for instance - but it should get all your events, albums and keywords, faces and places back.
Because this process creates an entirely new library and leaves your old one untouched, it is non-destructive, and if you're not happy with the results you can simply return to your old one.  
Regards
TD